In cases where a large number of individual telephone channels need to be provided between two geographical locations, it is common to multiplex a number of such channels on a single wide bandwidth circuit that extends between the locations. Multiplexing equipment is then provided at each location. This is done primarily to reduce the cost of providing transmission link for a large number of channels between the two locations.
An example is a loop carrier system provided between a large telephone company central office and a concentration of individual telephone subscribers located at least several miles away. A high bandwidth communications circuit is provided from the central office to the customer location, with a multiplexing terminal at each end. The use of a fiber optic transmission media between the terminals has an advantage over the use of a single electrical circuit in its greater bandwidth; that is, optical fiber systems can carry a much greater number of individual telephone channels. The channels are time multiplexed onto a single optical fiber transmission medium by providing repetitive time slots in sequence that are dedicated to each channel. Each terminal, therefore, provides for inserting signals from each channel being transmitted into its unique fiber optic time slot, and directs each received time slot to the correct individual telephone circuit. Each terminal includes a time slot inter-changer that allows control of which end user telephone channels are assigned to which time slots in the fiber optic transmission system.
Each such terminal must be capable of interconnecting with any one of several standard types of end user telephone circuits. A most common type is a circuit carrying a single telephone channel which is connected to a standard telephone instrument, computer terminal modem, and the like. Another common circuit, long designated as a T1 carrier system, carries 24 individual telephone channels. The T1 circuit eventually terminates each of its channels with a telephone subscriber. Since such systems are already widely in use, it is necessary to be able to connect them with the fiber optic trunk line. Other standards providing 12, 48 and 96 channels on a single wired telephone circuit also exist and must be connectable to such a communications terminal.
Therefore, it is a primary object of the present invention to provide a terminal system and components thereof that provides an ability for easily accommodating any of a wide variety of existing telephone subscriber circuits while utilizing the full bandwidth capability of the system.